Re: [PATCH V2 3/3] cpufreq: initialize governor for a new policy under policy->rwsem

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Tuesday, March 04, 2014 11:44:01 AM Viresh Kumar wrote:
> policy->rwsem is used to lock access to all parts of code modifying struct
> cpufreq_policy but wasn't used on a new policy created from __cpufreq_add_dev().
> 
> Because of which if we call cpufreq_update_policy() repeatedly on one CPU and do
> offline/online of another CPU then we might see these crashes:
> 
> Unable to handle kernel NULL pointer dereference at virtual address 00000020
> pgd = c0003000
> [00000020] *pgd=80000000004003, *pmd=00000000
> Internal error: Oops: 206 [#1] PREEMPT SMP ARM
> 
> PC is at __cpufreq_governor+0x10/0x1ac
> LR is at cpufreq_update_policy+0x114/0x150
> 
> ---[ end trace f23a8defea6cd706 ]---
> Kernel panic - not syncing: Fatal exception
> CPU0: stopping
> CPU: 0 PID: 7136 Comm: mpdecision Tainted: G      D W    3.10.0-gd727407-00074-g979ede8 #396
> 
> [<c0afe180>] (notifier_call_chain+0x40/0x68) from [<c02a23ac>] (__blocking_notifier_call_chain+0x40/0x58)
> [<c02a23ac>] (__blocking_notifier_call_chain+0x40/0x58) from [<c02a23d8>] (blocking_notifier_call_chain+0x14/0x1c)
> [<c02a23d8>] (blocking_notifier_call_chain+0x14/0x1c) from [<c0803c68>] (cpufreq_set_policy+0xd4/0x2b8)
> [<c0803c68>] (cpufreq_set_policy+0xd4/0x2b8) from [<c0803e7c>] (cpufreq_init_policy+0x30/0x98)
> [<c0803e7c>] (cpufreq_init_policy+0x30/0x98) from [<c0805a18>] (__cpufreq_add_dev.isra.17+0x4dc/0x7a4)
> [<c0805a18>] (__cpufreq_add_dev.isra.17+0x4dc/0x7a4) from [<c0805d38>] (cpufreq_cpu_callback+0x58/0x84)
> [<c0805d38>] (cpufreq_cpu_callback+0x58/0x84) from [<c0afe180>] (notifier_call_chain+0x40/0x68)
> [<c0afe180>] (notifier_call_chain+0x40/0x68) from [<c02812dc>] (__cpu_notify+0x28/0x44)
> [<c02812dc>] (__cpu_notify+0x28/0x44) from [<c0aeed90>] (_cpu_up+0xf4/0x1dc)
> [<c0aeed90>] (_cpu_up+0xf4/0x1dc) from [<c0aeeed4>] (cpu_up+0x5c/0x78)
> [<c0aeeed4>] (cpu_up+0x5c/0x78) from [<c0aec808>] (store_online+0x44/0x74)
> [<c0aec808>] (store_online+0x44/0x74) from [<c03a40f4>] (sysfs_write_file+0x108/0x14c)
> [<c03a40f4>] (sysfs_write_file+0x108/0x14c) from [<c03517d4>] (vfs_write+0xd0/0x180)
> [<c03517d4>] (vfs_write+0xd0/0x180) from [<c0351ca8>] (SyS_write+0x38/0x68)
> [<c0351ca8>] (SyS_write+0x38/0x68) from [<c0205de0>] (ret_fast_syscall+0x0/0x30)
> 
> Fix these by taking locks at appropriate places in __cpufreq_add_dev() as well.
> 
> Reported-by: Saravana Kannan <skannan@codeaurora.org>
> Suggested-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

I've rebased this one on top of 3.14-rc5 and queued it up for 3.14-rc6.

Please check the bleeding-edge branch for the result.

> ---
> V1->V2: No change
> 
>  drivers/cpufreq/cpufreq.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 3c6f9a5..e2a1e67 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1128,6 +1128,7 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
>  		policy->user_policy.max = policy->max;
>  	}
>  
> +	down_write(&policy->rwsem);
>  	write_lock_irqsave(&cpufreq_driver_lock, flags);
>  	for_each_cpu(j, policy->cpus)
>  		per_cpu(cpufreq_cpu_data, j) = policy;
> @@ -1202,6 +1203,7 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
>  		policy->user_policy.policy = policy->policy;
>  		policy->user_policy.governor = policy->governor;
>  	}
> +	up_write(&policy->rwsem);
>  
>  	kobject_uevent(&policy->kobj, KOBJ_ADD);
>  	up_read(&cpufreq_rwsem);
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.